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Diagram of slalom course including entrance gates (x), skier path and buoys 1–6 (o) and sample dimensions. 3 

Diagram of slalom course including entrance gates (x), skier path and buoys 1–6 (o) and sample dimensions. 3 

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Water skiing has received little attention in research literature and has not utilized recent advancements in analysis technology like other highly dynamic sports. In this study, six advanced slalom skiers were recruited to test four different high-performance ski designs, with the goal being to detect performance differences achieved between ski d...

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... skiing has approximately 10 million annual North American participants and growing international participation, evident by its introduction to the Pan Am Games in 1995. 1,2 Despite its growing popu- larity, water skiing requires equipment that is costly in terms of capital and ongoing running costs, combined with access to a suitable body of water, giving it the reputation of being a luxury sport. Slalom skiing, while an international competitive sporting event, is also considered to be an intermediate/ advanced recreational skiing activity in which the objective is to complete a course consisting of a series buoys. In this course, the skier must perform a sequence of oscillating left and right turns to travel on the outside of the buoys. The dimensions of the course are standar- dized but the activity can be made increasingly difficult by increasing boat speed and decreasing rope length. A basic slalom turn involves a complex sequence of motions that occur in a relatively short amount of time. Given the characteristics of the course, rope and boat, the success in performing this activity is dependent on the available ski performance and the skill and strength of the athlete. Historically, success was based on the number of marker buoys successfully completed, 3 and coaching was primarily by qualitative optical analysis. 4 Within the mechanics of the activity, however, there are a number of performance parameters that may be closely tied to overall success. Ski acceleration, deceleration and orientation are a few of the important performance parameters that may be closely tied to overall success and could be used to improve product development and coaching techniques. It is important to consider parameters such as ski acceleration, deceleration and orientation indepen- dently but also how they interact. It is hypothesized that a higher resultant in some of the parameters will be due to a higher resultant of another. For example, higher peak roll will lead to higher deceleration, which in turn leads to higher rope load and acceleration. To help identify which of the parameters are dependent on others, it is necessary to break down the different phases of a slalom cut and what reactions are taking place in each phase. Previous research into slalom water skiing performance, ski design and skier ability level has been limited to parameters such as ski rope load, 5,6 skier velocity 5,6 and overall slalom course success. 6 One additional study published a description of instrumentation that could be used to collect a variety of rope-based performance parameters. However, the authors were unable to support their work with any experimental data. 7 It seems apparent then that the advancement of strategies for water skiing performance analysis would ben- efit from the development and study of instrumentation and performance measures. This article is the third in a series of papers documenting the results of a research program investigating skiing performance biomechanics. Previously we have presented the initial study results 6 and instrumentation development details 8 for the overall study. The goal was to provide measurement tools and analysis strategies to quantitatively analyze water skiing biomechanics and performance. This article provides details of the methodology that was used to collect and analyze ski-based experimental data and performance parameter–based results of a group of advanced slalom skiers. This study was reviewed and received ethics approval for its subject participation and written survey compo- nents by the University of Guelph Ethics Committee. Six male water skiers (Table 1) capable of making two passes of a regulation slalom course on four different slalom skis were recruited for the study. Data collection was carried out over 3 days. Each experimental trial consisted of initializing the data collection program with the ski and skier on the dock. Then, the skier was taken to one end of a regulation slalom course 3 where he performed a deep water start, followed by two passes of the course (Figure 1). A pass of the course consists of a set-up cut, entrance cut where the skier enters the course through the entrance gates, followed by an oscillating sequence of six left and right turns (three of each) before exiting the course through the exit gates. To accommodate the use of unfamiliar skis, when a skier missed a marker, instead of it resulting in the entire pass being considered unsuccessful, as is the case in normal slalom competition, 3 skiers were encouraged to continue through the course, after which the missed markers would be tallied for later analysis. Each subject was still required to ski the length of the course and complete as many ‘‘good’’ slalom cuts as possible. The number of completed turns around the buoys was recorded as a performance parameter. After completing each of their trials, skiers were asked to complete the corresponding section of a written survey subjectively ranking the performance of the skis. Skis were instrumented with an inertial measurement unit (IMU; 3DM-GX2; Microstrain, Inc., Williston, VT, USA) weighing 16.7 N (dry weight including mounting hardware) mounted directly in front of the front binding. A custom fabricated plate was fastened to the ski, using the same bolt footprint as the front binding, and extended out towards the ski tip. The IMU housing was wrapped in plastic and strapped to the plate. Data from the sensor were transmitted, via custom radio frequency (RF) transmission system, to a computer (Acer Aspire One ZG5; Acer America Corporation, Mississauga, ON, Canada) located in the toe boat. The RF transmission system consisted of two custom-designed RF units, one located on the ski and the other was connected to the computer via universal serial bus (USB) port. Each unit had two RF transcei- ver modules (nRF2401; Nordic Semiconductor ASA, Tiller, Norway) that were operated by a microcontrol- ler. The data were parsed by the computer using a custom data collection program (LabVIEW 8.2; National Instruments Corporation, Austin, TX, USA). Rope load was measured using a load cell placed in series with the tow rope, skier speed was measured using a helmet-mounted 5-Hz Global Positioning System (GPS) unit and boat speed was measured using a 1-Hz GPS unit. Full details of the ski, skier and boat instrumentation have been published previously. 8 Each subject was required to perform one test run on each of the four skis. The skis varied in classification from ‘‘performance’’ to ‘‘tournament,’’ and all skis were commonly associated with advanced amateur and competitive level use. A brief summary of the skis can be found in Table 2 and ski profiles can be seen in Figure 2. A number of methods were incorporated to attempt to minimize unwanted data artifacts. A randomized testing order based on a Latin square design 9 was used to help minimize the effects of fatigue and changing weather throughout the day. To further minimize the factors that would influence the results, all of the ski runs were done on the same slalom course with a 17.9 m rope length. This rope when combined with the load cell instrumentation yielded an overall functional length of 18.25 m, equivalent to the international standard slalom competition rope length. 3 In addition, all of the ski runs were done with the same boat (1996, 5.7 l, MasterCraft Prostar 190; MasterCraft Boat Company, Cove Vonore, TN, USA) operating at 51.5 km/h (approximately equivalent to international competition standard boat speed for difficult conditions 3 ) for all experimental test runs (DigitalPro, PerfectPass; PerfectPass Control Systems Inc., Dartmouth, NS, Canada). Additionally, turn data were normalized for each skier’s forward foot. This resulted in the definition of dominant and nondominant turns where left foot forward skiers performed their dominant turns while on the port side of the slalom course (right turns), while right footed skiers performed their dominant turns while on the starboard side (left turns). Wind was monitored using a temporary weather station. Data were collected by a data logger (SynphoniePLUS; NRG Systems Inc., Hinesburg, VT, USA) from an anemometer (#40C, NRG Systems Inc.), located such that it was exposed to similar wind conditions as the slalom course. Data files were processed using Microsft Excel (Microsoft Canada Co., Mississauga, ON, Canada) after each of the test days. The orientation generated by the IMU was used to calculate pitch, roll and head- ing, which were then used to identify the left and right turns within each file. The quantitative threshold for a turn was defined as when ski roll passed through 0 ° of roll. For a left turn, the roll values were positive, and for a right turn, the values were negative. Individual turns were subdivided into five distinct phases: turn initiation, approach, apex, exit and wake crossing. A series of 11 performance parameters were identified and used for data analysis. The first of these was the Buoy Success Rate. Six ...

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